The present invention relates to an optically pumped far infrared laser having a resonator formed of at least three mirrors which are arranged in a vacuum-tight housing filled with laser gas and having furthermore a means for introducing a pump laser.
With optically pumped far infrared lasers (FIR laser) power stabilization generally presents a problem because a small portion of the pumping power introduced into the FIR laser resonator is reflected into the pump laser. This is known from carbon dioxide or nitrous oxide lasers, including doped embodiments. Accordingly, the standing wave resonators of FIR lasers and pump lasers are coupled to one another and can be viewed as a weakly coupled oscillating circuit. This coupling results in frequency and amplitude instabilities within the pump laser which results in strong amplitude fluctuations within the FIR laser. In practice, this so-called feed back coupling effect prevents an active frequency stabilization of the pump laser.
In order to realize a stable pump laser frequency and thus a stable output power for the FIR laser, an effective optical insulation of the pump laser and the FIR laser is an indispensable requirement. Because in many cases a pump laser within a wave length range between 9 and 11 .mu.m is to be used in order to provide f or a wide spectrum of FIR laser frequencies, universal broad range solutions are not realizable with classical polarization methods such as 1/4 wavelength platelets. Other methods, for example, insulation by acoustic-optical modulation or skewed introduction, result in a considerable loss of the pumping effectiveness.
From the journal article "Appl. Phys. Lett. 33 (7), 1. October 1978, S. 590-592" an FIR laser of the aforementioned kind is known which is called a ring laser and which is provided with a resonator with three mirrors embodied and arranged such that the laser beam is reflected from one mirror to the next in a ring-like fashion. For this open resonator the introduction of the pumping power is achieved with a special grate. With this known ring laser the feedback coupling effects of the pumping power are prevented; however, the open resonator results in considerable power losses. Furthermore, the introduction method used in the known device strongly depends on the wavelength of the pump laser and the ring laser.
It is therefore an object of the present invention to provide a laser of the aforementioned kind which has no feedback coupling effects and in which power losses are essentially prevented.